Pain-producing stimuli are detected by the nerve terminals of primary sensory neurons, whose cell bodies are found in sensory ganglia such as the dorsal root ganglia (DRG). The signal, in the form of action potentials, is transmitted along primary sensory nerve fibers to the dorsal horn of the spinal cord, and from there on to higher brain centers, where it is interpreted as pain. Primary sensory neurons can be activated by a wide range of thermal, mechanical and chemical stimuli. Injury or inflammation release a range of inflammatory mediators that increase the sensitivity of sensory neurons to noxious thermal or mechanical stimuli.
Interleukin IL-20 (IL-20) is a member of the IL-10 family, which includes IL-10, IL-19, IL-20, IL-22, IL-24, and IL-26. Blumberg, et al., 2001, Cell 104:9-19; Pestka et al., 2004, Annu Rev Immunol 22:929-979. IL-20 is expressed in monocytes, epithelial cells, and endothelial cells and acts on multiple cell types by activating a heterodimer receptor complex of either IL-20R1/IL-20R2 or IL-22R1/IL-20R2. Dumoutier, et al., 2001, J Immunol 167:3545-3549). IL-20 was found to be involved in various inflammatory diseases, such as psoriasis (Blumberg et al., 2001; Sa et al., 2007, J Immunol 178:2229-2240; and Wei et al., 2005, Clin Immunol 117:65-72), rheumatoid arthritis (Hsu, et al., 2006, Arthritis Rheum 54:2722-2733), atherosclerosis (Caligiuri, et al. 2006, Arterioscler Thromb Vasc Biol 26:1929-1930; and Chen et al., 2006, Arterioscler Thromb Vasc Biol 26:2090-2095), ischemic stroke (Chen et al., 2009, J Immunol 182:5003-5012), and renal failure (Li et al., 2008, Genes Immun 9:395-404). See also Wei et al., 2006, J Biomed Sci 13:601-612.